1. Field of the Invention
The present invention relates to a developing apparatus that develops an electrostatic image on an image bearing member, and more particularly to a developing apparatus preferably applied to an image forming apparatus such as a copier or a printer of the electrophotographic system, or a process cartridge detachably attachable to the image forming apparatus.
2. Related Background Art
Up to now, as a developing apparatus for use in an electrophotographic image forming apparatus such as a printer or a copier, as shown in FIG. 9, there has been proposed a developing apparatus having a process cartridge B detachably attachable to a main body of the electrophotographic image forming apparatus. Referring to FIG. 9, in the developing apparatus of this type, a magnet Mg is disposed within a hollow cylindrical developing roller 60c that functions as a developer bearing member, and its magnetic force allows a developer (hereinafter referred to as "toner") to be attracted onto the developing roller 60c. Then, with the rotation of the developing roller 60c (or the magnet Mg), the toner is carried to a developing section that allows a latent image to be visualized.
As a manner of preventing the toner from being leaked outward from a developing container 60b, there has been known a method in which a sealing member such as a felt is brought into contact with the developing roller outside of an image region, or as shown in FIG. 9, a ferromagnetic member 71 that functions as a sealing member is disposed out of contact with the developing roller 60c so that its magnetic force allows the toner to be held.
In addition, in order that the toner carried on the downstream side of the sealing member with the rotation of the developing roller 60c or the magnet Mg as described above is again returned within the developing region so as to be prevented from being leaked outwardly, a scraping member 72 is disposed on the downstream side of the above-described sealing member (the ferromagnetic member 71 in FIG. 9) in a direction along which the developing roller 60c rotates, and a part of the scraping member 72 is brought into contact with the developing roller 60c.
Also, in order to hold a distance between a photosensitive drum 57 and the developing roller 60c constant, there is applied a method in which both end portions of the developing roller 60c are covered with cap rollers (not shown) the thickness of which is severely managed.
However, in the above-described conventional example, there was a case in which when the toner scraped off by the scraping member 72 is over-deposited on the scraping member 72, the toner comes off from the developing roller 60c and flies up with the result that the toner is temporarily or permanently dispersed and exists in the form of a lump on a portion where the photosensitive drum 57 and the cap rollers are abutted against each other. In this case, when the rotation of the photosensitive drum 57 or the developing roller 60c permits a lump of the toner to come to a position where the photosensitive drum 57 and the cap rollers are in contact with each other, a distance between the photosensitive drum 57 and the developing roller 60c becomes rapidly larger than a given distance (the thickness of the cap rollers), thereby causing a case in which the distance made larger returns to the given distance after the lump of toner has passed between the photosensitive drum 57 and the developing roller 60c. This leads to a phenomenon (hereinafter referred to as "white banding") in which an image on a portion corresponding to the lump of toner is thinned.